An example of a conventional molded motor is described in U.S. Pat. No. 6,002,185 to Nakao, et al. The conventional molded motor described in U.S. Pat. No. 6,002,185 includes a stator, a rotor rotatably disposed inside the stator, bearings disposed at both ends of the rotor to support the rotor so that it can rotate freely, and a molded main body which covers the stator laminations. The stator includes a stator core laminated from a plurality of layers of cold-rolled steel plate, which is a ferrous material; stator coils composed of lead wires wound around tooth portions of the stator core, a first guide and second guide which fit into the stator core from the top and bottom respectively to insulate between the stator coils and the stator core, and a terminal fixed by heat crimping to the second guide and connected to the stator coils. The rotor is provided with a shaft supported at both ends by the bearings so that it can rotate freely and magnets fixed to the shaft with adhesive, arranged with alternating north-seeking (N) poles and south-seeking (S) poles. The molded main body has a connector portion, flange portions integrated with bushes into which bolts are inserted, and a receiving portion which receives an annulus, which is an inserted body. The molded motor is connected by means of bolts inserted into the bushes to a throttle valve device, which regulates the amount of air delivered to an internal combustion engine. In the molded motor of the above construction, an integrated motor main body is formed from the stator, the molded main body, and a bushing by injection molding in which a resin is injected into a metal mold in which the stator and the bushing have been placed. Then the bearing, which is secured to the shaft, is inserted into the bushing and the motor main body and the rotor are integrated, completing the assembly of the molded motor. The disclosure of the foregoing is incorporated by reference herein in its entirety.
In conventional processes for fabricating over molded motors, the motor main body is formed by injecting high-temperature resin into a metal mold. There are, however, disadvantages to current over molded assemblies which render the assemblies unsuitable for certain applications. One of the problems encountered with current over molded motors is that the molded main body plastic is disposed around the entire outside diameter of the stator laminations thereby insulating the motor and holding in heat. Another problem is encountered because the air gap between the rotor magnet and the motor stator laminations inside diameter needs to be very small for optimum performance. Flash resulting from the injection molding process along the inside diameter of the motor stator laminations restricts the motion of the rotor. If plastic were molded over the inside diameter of the stator laminations on purpose, it would reduce performance due to an increased air gap. Yet another drawback to currently available over molded motors relates to difficulties encountered when locating the motor within the metal housing. Plastic molded over the outside diameter reduces heat transfer out of the motor to the metal housing.
What is needed in the art is an improved process for fabricating an over molded motor stator structure. What is further needed in the art is an improved process for fabricating an over molded motor stator structure which can provide improved thermal transfer and thus heat dissipation as compared to currently available injection molded motors.